Metering devices are used to measure consumption of resources. Examples of metering devices include electricity meters, water meters, and gas meters. A metering device may communicate consumption of a given resource through a pulse source communicating with a pulse-counting device.
One common pulse source is a magnet positioned on a wheel and one common pulse-counting device is a reed switch. In an example meter device, a crankshaft causes the wheel to spin as the resource flows through the metering device. As the wheel spins, a magnet on the wheel passes by a reed switch, which generates a pulse. An electrical circuit connected to the reed switch counts the pulses and determines the amount of resource consumed. For example, in a meter device with one magnet, a rotation of the wheel causes one pulse. The number of pulses therefore equals the number of units of a particular volume of the resource that have been consumed.
But the use of reed switches in sensing designs can be problematic, because reed switches only indicate whether a magnetic field is present, and cannot detect small changes in magnetic field. As a consequence, a metering device using reed switches is susceptible to magnet bounce. Magnet bounce occurs when magnet bounces between clockwise and counterclockwise directions before coming to a stop. A reed switch cannot distinguish a magnet bouncing past that causes a small change in magnetic field from a magnet that has made a complete rotation.
Additionally, sensing designs that use reed switches are sensitive to external magnetic fields (for example, from tampering). Because a reed switch cannot measure small magnetic variations, a placement of an external magnetic field caused by a magnet designed to interfere with the measurement of the resource goes undetected. External magnetic fields can cause false activation of the reed switch when the dial wheel has not moved.
Reed switches are also sensitive to magnet misalignment, which can occur when the magnet, the sensor, or the wheel are misaligned. Because reed switches only allow for a very small amount of variation, reed switches can cause erroneous results to be measured if misalignment occurs.
Accordingly, improved meter sensor designs are needed.